A conventional tire air pressure monitoring apparatus, such as that disclosed in Japanese Patent No. 3,212,311, includes a sensor placed in each tire of a vehicle that measures air pressure in the tire and wirelessly transmits the measured value to a receiver provided on a vehicle body side. A receiver identifies the sensor transmitting the transmission data by an identification signal such as a unique previously assigned sensor ID contained in the transmission data and monitors the air pressure in the tire.
However, a problem may occur in the above described tire air pressure monitoring apparatus. When the sensor ID is registered in the receiver, the receiver is set to a registration mode and the transmission data is transmitted from the sensor to the receiver while it is in the registration mode. The sensor ID contained in this transmission data is stored in a memory and its registration is performed.
It is conceivable that the sensor ID registration is performed in many manufacture lines arranged in parallel as shown in FIG. 4, or also in a maintenance facility of a dealer or the like, in which the sensor ID registrations of a plurality vehicles are performed in places adjacent to each other. Therefore, the receiver may erroneously register the sensor ID of the sensor mounted in another vehicle during the registration mode when transmission data is transmitted from a sensor of another adjacent vehicle.